摘要
黑龙江穆棱地区赋存着大量与玄武岩有关的红宝石、蓝宝石矿床,其中黑色尖晶石通常作为副矿物开采。近年来,高品质的黑色尖晶石因颗粒大、光泽强引起人们的关注,但穆棱地区黑色尖晶石罕有报道。利用常规宝石学测试、光谱学测试以及化学成分测试,对黑龙江穆棱黑色尖晶石样品进行了较系统的宝石学特征探究。结果表明,黑龙江穆棱黑色尖晶石样品多具自形-半自形八面体晶形,不透明,表面存在蚀痕。显微镜下,样品内部可见熔体包裹体、硫化物包裹体、八面体包裹体等。化学成分结果显示,穆棱黑色尖晶石样品属于严格意义上的镁铝尖晶石,含有部分铁铝尖晶石、镁铁尖晶石和磁铁矿成分。高含量的Fe(14.97~26.37wt.%)导致样品呈现黑色且透明度低。穆斯堡尔谱测试结果表明,Fe在穆棱尖晶石样品中以Fe2+和Fe^(3+)两种价态存在,其中Fe^(3+)在其晶体结构中占据两个阳离子位置(四配位和六配位),Fe^(3+)的四次配位使得样品呈现部分反尖晶石结构。因此,穆棱黑色尖晶石样品的拉曼光谱不同于宝石级透明镁铝尖晶石的光谱,而是类似于尖晶石族其它矿物(如铬铁矿、磁铁矿)的光谱,主要以749 cm^(-1)和538 cm^(-1)处的强波数为特征,并在343、402、645、705 cm^(-1)处出现较小的峰或肩峰。
There are a large number of ruby and sapphire deposits related to basalt in Muling area,Heilongjiang Province,in which black spinel is usually mined as an accessory mineral.In recent years,high-quality black spinel has also attracted people’s attention because of its large particle size and strong lustre.However,there are few reports on black spinel in Muling area.In this paper,the gemmological characteristics of Muling black spinel were studied by conventional gemmological tests,spectroscopic tests and chemical composition tests.The results indicated that the black spinel samples from Muling predominantly exhibit euhedral to subhedral octahedral crystal shapes,opaque,and displays surface abrasions.Melt inclusions,sulfide inclusions,and octahedral inclusions are visible under the microscope.Muling black spinel belongs to magnesia alumina spinel in a strict sense,and contains some magnesioferrite and magnetite.The high content of iron(14.97-26.37 wt.%)causes mullite spinel to be black and completely impermeable.Mossbauer spectroscopic results showed that iron exists in spinel in two valence states of Fe 2+and Fe^(3+),in which Fe^(3+)occupies two cation positions(quaternary coordination and hexagonal coordination)in the crystal structure.The tetrahedral coordination of Fe^(3+)makes the spinel show some anti spinel structure.Therefore,the Raman spectrum of Muling black spinel is different from that of gem grade transparent magnesium aluminum spinel,but similar to that of other spinel minerals(such as chromite,magnetite).It is dominated by strong wave numbers at 749 cm^(-1) and 538 cm^(-1),with smaller peaks or shoulders occurring at about 343,402,645 cm^(-1) and 705 cm^(-1).
作者
佟雨佳
胡琳琳
潘少逵
TONG Yujia;HU Linlin;PAN Shaokui(Gemmological Institute,China University of Geosciences,Wuhan 430074,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Hube Gems and Jewelry Engineering Technology Research Center,Wuhuan 430074,China)
基金
国家自然科学基金—佳木斯地块岩石圈地幔的性质及演化(41973032)。
关键词
尖晶石
显微特征
化学成分
穆斯堡尔谱
黑龙江穆棱
spinel
microscopic characteristic
chemical composition
M ssbauer spectroscopy
Muling,Heilongjiang Province
